Interface, a method for observing an object within a non-vacuum environment and a scanning electron microscope

ABSTRACT

An interface, a scanning electron microscope and a method for observing an object that is positioned in a non-vacuum environment. The method includes: passing at least one electron beam that is generated in a vacuum environment through at least one aperture out of an aperture array and through at least one ultra thin membrane that seals the at least one aperture; wherein the at least one electron beam is directed towards the object; wherein the at least one ultra thin membrane withstands a pressure difference between the vacuum environment and the non-vacuum environment; and detecting particles generated in response to an interaction between the at least one electron beam and the object.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/302,221, filed Jun. 11, 2015, which is a continuation of U.S. patentapplication Ser. No. 13/449,392, filed Apr. 18, 2012, now issued as U.S.Pat. No. 8,779,358 on Jul. 15, 2014, which is a continuation of U.S.patent application Ser. No. 12/446,757, filed Jan. 24, 2010, now issuedas U.S. Pat. No. 8,164,057 on Apr. 24, 2012, which is a national phaseof International Application No. PCT/IL2007/001265, filed Oct. 23, 2007,which in turn claims priority from U.S. Provisional Patent ApplicationNo. 60/862,631, filed Oct. 24, 2006. All disclosures of the documentsnamed above are incorporated herein by reference.

BACKGROUND

1. Field of the Invention

High resolution microscopy is used in research and development, qualityassurance and production in diverse fields such as material science,life science, the semiconductor industry and the food industry.

2. Description of the Related Art

Optical microscopy dating back to the seventeenth century, has reachedits brick wall, defined by the wavelength of deep Ultra Violet photons,giving a finest resolution of about 80 nm. The popularity of opticalmicroscopy stems from its relative low price, ease of use and thevariety of imaging environment all translated to availability.

Scanning electron microscopy provides a much finer resolution (even fewnanometers) but in order to achieve that high resolution the inspectedobject should be placed in a vacuum environment.

U.S. Pat. No. 6,992,300 of Moses titled “Device and method for theexamination of samples in a non-vacuum environment using a scanningelectron microscope” describes a chamber that includes an ultra thinmember that can withstand a vacuum and is transparent to electrons. Thethickness of the membrane is arguably few hundred Angstrom.

Due to mechanical constraints, using an ultra thin membrane impliessmall supporting aperture. The small size of the ultra thin membranedramatically reduces the throughput of the scanning electron microscopeand renders such a scanning electron microscope impractical.

There is a growing need to provide fast and accurate scanning electronmicroscopes.

SUMMARY OF THE INVENTION

A method for observing an object that is positioned in a non-vacuumenvironment, the method includes: passing at least one electron beamthat is generated in a vacuum environment through at least one apertureout of an aperture array and through at least one ultra thin membranethat seals the at least one aperture; wherein the at least one electronbeam is directed towards the object; wherein the at least one ultra thinmembrane withstands a pressure difference between the vacuum environmentand the non-vacuum environment; and detecting particles generated inresponse to an interaction between the at least one electron beam andthe object.

Conveniently, the passing includes passing at least one electron beamthrough multiple apertures of the aperture array.

Conveniently, the passing is preceded by selecting an aperture of theaperture array and wherein the passing includes passing an electron beamthrough the selected aperture.

Conveniently, the method includes passing at least one electron beamthrough at least one aperture of the aperture array wherein apertures ofthe aperture array are positioned at a single horizontal plain.

Conveniently, the method includes passing at least one electron beamthrough at least one aperture of the aperture array; and wherein atleast one aperture of the aperture array is positioned at a differentheight than at least one other aperture of the aperture array.

Conveniently, the method includes passing at least one electron beamthrough at least one aperture of the aperture array; and wherein atleast one aperture of the aperture array enables an acquisition of ahigher resolution image than at least one other aperture of the aperturearray.

Conveniently, the method includes performing a first iteration ofpassing and detecting and a second iteration of passing and detecting;wherein the first phase includes passing at least one electron beamthrough at least one aperture to provide a first resolution image of atleast a portion of the object, and the second phase includes passing atleast one electron beam through at least one other aperture to provide asecond resolution image of at least a portion of the object.

Conveniently, the passing is preceded by locating a region of interestof the object using a low resolution imaging process; and the passingincludes passing at least one electron beam directed towards the regionof interest.

Conveniently, the passing and detecting are characterized by a firstresolution range and wherein the method further includes utilizinganother observation process that is characterized by a differentresolution range.

Conveniently, the other observation process includes atomic forcemicroscopy.

Conveniently, the other observation process includes an opticalinspection process.

Conveniently, the method further includes scanning at least one area ofthe object by deflecting the at least one electron beam and introducinga corresponding mechanical movement of the at least one aperture throughwhich the at least one electron beam pass.

Conveniently, the method includes scanning at least one area of theobject by deflecting the at least one electron beam and introducing acorresponding mechanical movement of the aperture array.

Conveniently, the method includes scanning at least one area of theobject by deflecting the at least one electron beam and introducing acorresponding mechanical movement of the aperture array; wherein acomponent that includes is flexibly coupled to another component of aninterface that separates the vacuum environment from the non-vacuumenvironment. Conveniently, the method includes scanning multiple areasof the object

by deflecting the at least one electron beam that pass through multipleapertures of the aperture array.

Conveniently, the method includes scanning multiple areas of the objectby deflecting the at least one electron beam that pass through multipleapertures of the aperture array and introducing a correspondingmechanical movement of the aperture array.

Conveniently, the method includes scanning an area of the object bydeflecting the at least one electron beam by a deflector positionedwithin the vacuum environment.

Conveniently, the method includes detecting electrons generated inresponse to the interaction between the at least one electron beam andthe object.

Conveniently, the method includes detecting photons generated inresponse to the interaction between the at least one electron beam andthe object.

Conveniently, the method includes detecting X-ray emission generated inresponse to the interaction between the at least one electron beam andthe object.

Conveniently, the method includes detecting particles by a detectorpositioned within the vacuum environment.

Conveniently, the method includes detecting particles by a detectorpositioned within the non-vacuum environment.

Conveniently, an optical axis of the at least one electron beam isnon-perpendicular to the object.

Conveniently, the method includes detecting electron current generatedas a result of the interaction.

Conveniently, the method includes detecting Cathodoluminescence of theobject, fluorescence markers or light emitted due to electron excitationof gas molecules.

Conveniently, the method includes introducing a gas mixture into thenon-vacuum environment such as to improve the detecting.

Conveniently, the method includes introducing nitrogen into thenon-vacuum environment.

Conveniently, the method includes introducing He enriched mixture intothe non-vacuum environment.

Conveniently, the method includes aligning the at least one electronbeam with at least one aperture.

Conveniently, the method includes aligning the at least one electronbeam with at least one aperture by introducing a mechanical moving theat least one aperture.

Conveniently, the method includes repetitively altering a distancebetween an aperture and the object and measuring electrons emitted fromthe object to provide measurements results and comparing the measurementresults to a calibration curve that is responsive to a mean free path ofelectrons in the non-vacuum environment.

Conveniently, the method includes determining a distance between anaperture and the object based upon an expected mean free path ofelectrons in the non-vacuum environment.

Conveniently, the method includes determining a distance between anaperture and the object based upon counts of emitted X-ray photons ofgas within the non-vacuum environment that is situated between theobject and the aperture.

A method for observing an object that is positioned in a non-vacuumenvironment, the method includes: scanning at least one area of theobject by: deflecting at least one electron beam generated in a vacuumenvironment and allowing the at least one electron beam to pass throughat least one aperture sealed by an ultra thin membrane; wherein the atleast one ultra thin membrane withstands a pressure difference betweenthe vacuum environment and the non-vacuum environment; and introducing acorresponding mechanical movement of the at least one aperture; anddetecting particles generated in response to an interaction between theat least one electron beam and the at least one area of the object.

An interface between a vacuum environment and a non-vacuum environment,the interface includes an aperture array sealed by at least one ultrathin membrane that is substantially transparent to electrons andwithstands a pressure difference between the vacuum environment and thenon-vacuum environment.

Conveniently, apertures of the aperture array are positioned at a singlehorizontal plain.

Conveniently, at least one aperture of the aperture array is positionedat a different height than at least one other aperture of the aperturearray.

Conveniently, at least one aperture of the aperture array enables anacquisition of a higher resolution image than at least one otheraperture of the aperture array.

A scanning electron microscope includes: an electron beam sourcepositioned in a vacuum environment; the electron beam source is adaptedto generate at least one electron beam; an interface between the vacuumenvironment and a non-vacuum environment in which an object ispositioned, the interface includes an aperture array sealed by at leastone ultra thin membrane that is substantially transparent to electronsand withstands a pressure difference between the vacuum environment andthe non-vacuum environment; electron optics adapted to direct the atleast one electron beam through at least one aperture and towards anobject located in the non-vacuum environment; and a detector thatdetects particles generated in response to an interaction between the atleast one electron beam and the object.

Conveniently, the electron optics directs at least one electron beamtowards multiple apertures of the aperture array.

Conveniently, the scanning electron microscope is adapted to select anaperture of the aperture array and wherein then direct an electron beamthrough the selected aperture.

Conveniently, apertures of the aperture array are positioned at a singlehorizontal plain.

Conveniently, at least one aperture of the aperture array is positionedat a different height than at least one other aperture of the aperturearray.

Conveniently, at least one aperture of the aperture array enables anacquisition of a higher resolution image than at least one otheraperture of the aperture array.

Conveniently, the scanning electron microscope is adapted to direct atleast one electron beam through at least one aperture to provide a firstresolution image of at least a portion of the object, and then direct atleast one electron beam through at least one other aperture to provide asecond resolution image of at least a portion of the object.

Conveniently, the scanning electron microscope is adapted to locate aregion of interest of the object using a low resolution imaging processand then direct at least one electron beam towards the region ofinterest.

Conveniently, the scanning electron microscope another observation toolthat is characterized by another resolution that the resolution providedby the electron beam.

Conveniently, the other observation tool is an atomic force microscope.

Conveniently, the other observation tool is an optical inspection tool.

Conveniently, the scanning electron microscope is adapted to scan atleast one area of the object by deflecting the at least one electronbeam and introducing a corresponding mechanical movement of the at leastone aperture through which the at least one electron beam pass.

Conveniently, the scanning electron microscope is adapted to scan atleast one area of the object by deflecting the at least one electronbeam and introduce a corresponding mechanical movement of the aperturearray.

Conveniently, the scanning electron microscope is adapted to scan atleast one area of the object by deflecting the at least one electronbeam and introduce a corresponding mechanical movement of the aperturearray; wherein a component that includes the aperture array is flexiblycoupled to another component of an interface that separates the vacuumenvironment from the non-vacuum environment.

Conveniently, the scanning electron microscope is adapted to scanmultiple areas of the object by deflecting the at least one electronbeam that pass through multiple apertures of the aperture array.

Conveniently, the scanning electron microscope is adapted to scanmultiple areas of the object by deflecting the at least one electronbeam that pass through multiple apertures of the aperture array andintroducing a corresponding mechanical movement of the aperture array.

Conveniently, the scanning electron microscope includes a deflector thatis positioned within the vacuum environment that deflects the at leastone electron beam such as to scan an area of the object.

Conveniently, the detector detects electrons generated in response tothe interaction between the at least one electron beam and the object.

Conveniently, the detector detects photons generated in response to theinteraction between the at least one electron beam and the object.

Conveniently, the detector detects X-ray emission generated in responseto the interaction between the at least one electron beam and theobject.

Conveniently, the detector is positioned within the vacuum environment.

Conveniently, the detector is positioned within the non-vacuumenvironment.

Conveniently, an optical axis of the at least one electron beam isnon-perpendicular to the object.

Conveniently, the detector detects electron current generated as aresult of the interaction.

Conveniently, the detector detects Cathodoluminescence of the object,fluorescence markers or light emitted due to electron excitation of gasmolecules.

Conveniently, the scanning electron microscope is adapted to introduce agas mixture into the non-vacuum environment such as to improve thedetecting.

Conveniently, the scanning electron microscope is adapted to introducenitrogen into the non-vacuum environment.

Conveniently, the scanning electron microscope is adapted to introduceHe enriched mixture into the non-vacuum environment.

Conveniently, the scanning electron microscope is adapted to align theat least one electron beam with at least one aperture.

Conveniently, the scanning electron microscope is adapted to align theat least one electron beam with at least one aperture by introducing amechanical movement the at least one aperture.

Conveniently, the scanning electron microscope is adapted torepetitively alter a distance between an aperture and the object,measure electrons emitted from the object to provide measurementsresults and compare the measurement results to a calibration curve thatis responsive to a mean free path of electrons in the non-vacuumenvironment.

Conveniently, the scanning electron microscope is adapted to determine adistance between an aperture and the object based upon an expected meanfree path of electrons in the non-vacuum environment.

Conveniently, the scanning electron microscope is adapted to determine adistance between an aperture and the object based upon counts of emittedX-ray photons of gas within the non-vacuum environment that is situatedbetween the object and the aperture.

An interface between a vacuum environment and a non-vacuum environment,the interface includes at least one aperture sealed by at least oneultra thin membrane that is substantially transparent to electrons andwithstands a pressure difference between the vacuum environment and thenon-vacuum environment; wherein a component that includes the at leastone aperture is flexibly coupled to another component of the interface.

Conveniently, the aperture includes an aperture array and whereinapertures of the aperture array are positioned at a single horizontalplain.

Conveniently, the aperture includes an aperture array and wherein atleast one aperture of the aperture array is positioned at a differentheight than at least one other aperture of the aperture array.

Conveniently, the aperture includes an aperture array and wherein atleast one aperture of the aperture array enables an acquisition of ahigher resolution image than at least one other aperture of the aperturearray.

A scanning electron microscope includes: an electron beam sourcepositioned in a vacuum environment; the electron beam source is adaptedto generate at least one electron beam; an interface between a vacuumenvironment and a non-vacuum environment, the interface includes atleast one aperture sealed by at least one ultra thin membrane that issubstantially transparent to electrons and withstands a pressuredifference between the vacuum environment and the non-vacuumenvironment; wherein a component that includes the at least one apertureis flexibly coupled to another component of the interface; electronoptics adapted to direct the at least one electron beam through at leastone aperture and towards an object located in the non-vacuumenvironment; and a detector that detects particles generated in responseto an interaction between the at least one electron beam and the object.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects and advantages of the invention will becomeapparent and more readily appreciated from the following description ofthe embodiments, taken in conjunction with the accompanying drawings ofwhich:

FIG. 1 illustrates a system according to an embodiment of the invention;

FIGS. 2 a and 2 b illustrate systems according to two embodiments of theinvention;

FIGS. 3 a and 3 b illustrate systems according to two embodiments of theinvention;

FIGS. 4 a and 4 b are a top view and a side view of an aperture arrayand multiple membranes according to an embodiment of the invention;

FIGS. 5 a and 5 b illustrate two aperture arrays according to variousembodiments of the invention;

FIGS. 6 a-6 f illustrates an area of an object and multiple images thatimage the entire area according to an embodiment of the invention;

FIGS. 7 a and 7 b are images of multiple sub-areas of an object and animage of a single sub-area obtained via an aperture array according toan embodiment of the invention;

FIG. 8 illustrates multiple apertures and multiple membranes accordingto an embodiment of the invention;

FIGS. 9 a-9 c illustrates an aperture array, flexible connector andmotor, according to various embodiments of the invention;

FIG. 10 illustrates a system integrated with another tool according toan embodiment of the invention;

FIGS. 11-14 are flow charts of methods according to various embodimentsof the invention;

FIGS. 15 a-15 c illustrate multiple positions of an aperture andmultiple electrical beam orientations during a scan according to anembodiment of the invention;

FIGS. 16 a-16 b are images of wafer with contacts imaged in air;

FIG. 17 is an image of a Cu test structure imaged in air; and

FIGS. 18 a-18 c are images of an aperture and of a grid imaged in airaccording to an embodiment of the invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

According to an embodiment of the invention the throughput of a scanningelectron microscope that observes an object (positioned in a non-vacuumenvironment) is increased by illuminating multiple apertures (sealed byone or more membranes) simultaneously. These multiple apertures can forman aperture array or can be a part of an aperture array.

According to an embodiment of the invention one or more areas of aninspected object (positioned in a non-vacuum environment) are scanned bydeflecting one or more electron beams and also introducing acorresponding mechanical movement of one or more apertures through whichthe one or more electron beams pass. This combination of deflection andmechanical movement increases the field of view of the system.

According to yet another embodiment of the invention multiple aperturesthat are sealed by one or more membranes are provided. The apertures andthe membranes can differ by their size and thickness (of membranes) thusproviding different compromises between field of views and resolution.

The term aperture array means any arrangement (ordered or non-ordered)of apertures.

Conveniently, the ultra thin membrane is thinner then few tens ofnanometers and is made of low density material such as Carbon or SiN.

When multiple apertures are provided each aperture can be sealed by itsown membrane, although this is not necessarily so. A single membrane canseal multiple apertures. According to an embodiment of the invention themembrane can be connected to a very thin grid that defines multipleapertures.

The ultra thin membrane seals an aperture while withstanding thepressure difference between the vacuum environment and the non-vacuumenvironment.

The ultra thin membrane is used because it has the minimal impact on theelectron spot size. For better performance it is advantageous to usehigher electron accelerating voltages, preferably 20 kV and higher.Another advantage of using ultra thin membrane is that the electronsused to generate the image can be efficiently collected with detectorssituated in the vacuum environment.

Electrons interact with the inspected object and various particles areformed. Particles such electrons or photons can be detected. Detectionsignals from one or more detectors can be processed in order to providean image of the object.

According to an embodiment the system can provide different field ofviews. Different apertures and different membranes can be of differentsize and thickness. Different membranes can be located at differentheights. Low resolution and low magnification can be provided by thickermembranes and larger apertures. High resolution can be provided bythinner membranes and smaller apertures. One or more apertures andmembranes can be selected by either mechanically moving these one ormore apertures towards the electron beam axis, and additionally oralternatively, using deflectors to deflect the electron beam to thedesired aperture.

Conveniently, a large field of view can assist in navigation and findinga region of interest. The extended field of view can be obtained byutilizing multiple apertures that are separated from each other. Even ifthe multiple apertures do not provide a continuous image of an imagedarea this can suffice for navigation or region of interest location.

According to various embodiments of the invention an object can beilluminated by multiple electron beams. It is noted that an electronbeam can be spilt by the aperture array that is sealed with one or moremembranes. It is further noted that multiple electron beams can bedirected towards the aperture array. These multiple electron beams canbe further split by the aperture array but this is not necessarily so aseach electron beam can be directed toward a specific aperture.

For simplicity, some of the following explanations refer to a singleelectron beam. Those of skill in the art will appreciate thatexplanations that refer to a single electron beam can also be appliedmutatis mutandis to multiple electron beams.

For simplicity, some of the following explanations refer to a singleaperture (membrane). Those of skill in the art will appreciate thatexplanations that refer to a single aperture (membrane) beam can also beapplied mutatis mutandis to multiple apertures (membranes).

FIG. 1 illustrates system 30 according to an embodiment of theinvention.

System 30 (also referred to as SEM 30) includes: (i) scanning electronmicroscope column 1 that generates, accelerates, scans and focuses anelectron beam 2; (ii) an interface 3 that includes one or more aperturesthat are sealed by one or more membranes; (iii) a sample holder (notshown) that is connected to optional mechanical stage 7; (iv) computer16, (v) controller 17, (vi) high voltage supply 18, (vii) low powersupply and scanner 19, (viii) data acquisition and image grabber 20,(ix) one or more pumps 15; and (x) one or more detectors such as but notlimited to spectrometer controller and processor 21, side electrondetector 8 (for detecting low energy electrons 12), center electrondetector 9 (for detecting high energy electrons 13), a photon detectoror spectrometer 10 (for detecting photons 14), a Pico ampere meter 11(that measures a current generated as a response to an interactionbetween electron beam 2 and object 6). It is noted that only one of fewof the mentioned above detectors can be included in system 30.

System 30 can generate an image of object 6, a two dimensional map ofobject 6, perform a point analysis or provide a spectrum. Computer 16and controller 17 control the parameters and operation of variouscomponents of system 30.

Vacuum environment is denoted 4 while the non-vacuum environment isdenoted 5.

Conveniently, electron beam 2 is directed towards object 6 such as topass through one or more apertures of interface 3 and to impinge ontoobject 6. The impinging electrons generate secondary electrons,backscattered electrons, characteristic X-rays and in some casesCathodoluminescence. The Cathodoluminescence can be either a surfaceproperty or due to light emission from markers or labeling molecules.The emitted signal is detected with the aid of one of the mentionedabove detectors.

FIGS. 2 a and 2 b illustrate systems 31 and 32 according to twoembodiments of the invention. FIG. 2 a illustrates a single assemblythat includes SEM column 1, detectors 4, 5 and 6 and interface 3.

FIG. 2 b illustrates an adaptor chamber 102 that is connected to SEM101. SEM 101 can work without adaptor chamber 102 and can be anyavailable SEM in the market. Adaptor chamber 102 maintains a vacuumenvironment and includes detectors 4, 5 and 6, interface 3 and a SEMinterface 103 that can be connected to SEM 101 and seal SEM 101 from thenon-vacuum environment in which object 6 is located.

FIGS. 3 a and 3 b illustrate systems 33 and 34 according to twoembodiments of the invention.

FIG. 3 a illustrates an adaptor chamber 103 that is connected to SEM101. SEM 101 can work without adaptor chamber 101 and can be anyavailable SEM in the market.

Non-vacuum chamber 104 is located inside adaptor chamber 103 or is atleast partially surrounded by adaptor chamber 103. Adaptor chamber 103maintains a vacuum environment and includes detectors 4, 5 and 6,interface 3 and a SEM interface 103 that can be connected to SEM 101 andseal SEM 101 from non-vacuum chamber 104 in which object 6 is located.

FIG. 3 b illustrates system 34 that includes a tilted SEM column 1′ thatilluminates object 6 in a titled (non-perpendicular manner). SEM column1′ can be stationary or can be rotated (optionally to a non-tiltedposition) in order to alter the angle between its optical axis andsample 6.

Aperture Array

The aperture array can include an aperture array of different sizes thatare sealed by membranes of different areas and thickness. The differentapertures can be positioned at the same plane, as illustrated in FIG. 4but this is not necessarily so. For example, apertures and membranes canbe positioned in a staggered manner, as illustrated in FIG. 8.

FIGS. 4 a and 4 b illustrate an aperture array 60 that includes threeapertures 61, 62, and 63 and corresponding membranes 71, 72 and 73. FIG.4 a is a top view of aperture array 60 while FIG. 4 a is a side view ofaperture array 60. The biggest aperture is aperture 61 and its membrane(membrane 71) is the thickest. The smallest aperture is aperture 62 andits membrane (membrane 72) is the thinnest. The area of aperture 63 issmaller than the area of aperture 61 but bigger that the area ofaperture 63. Accordingly, its corresponding membrane (membrane 73) isthinner than membrane 71 but thicker than membrane 72. The threeapertures and membranes are positioned in the same plane. Theseapertures can be illuminated concurrently or separately.

Larger apertures should be sealed by thicker membranes. Larger aperturesprovide larger field of view but thicker membranes reduce theresolution. Accordingly, a system that includes membranes of differentthickness and apertures of different areas can provide multipletrade-offs between field of views and resolution.

The different apertures can be accessed by moving the apertures to theelectron beam position, and/or by deflecting the electron beam.

According to another embodiment of the invention an aperture arrayincludes evenly sized apertures and conveniently evenly sized membranes.

FIGS. 5 a and 5 b illustrate aperture arrays 81 and 82. Aperture array81 includes rectangular apertures while aperture array 82 includescircular apertures. It is noted that a single aperture array can includeapertures of different shaped apertures.

An entire area of the object can be imaged by scanning that area by anaperture array. The scanning axis can be parallel a longitudinal axis ora latitudinal axis of the aperture array but can also oriented inrelation to these arrays. Referring to aperture array 81 of FIG. 4—thescan axis can be horizontal (parallel to a latitudinal axis of aperturearray 81), can be vertical (parallel to a longitudinal axis of aperturearray 81) or can be oriented to these axes.

It is noted that when virtually combining the field of view provided byeach of the apertures a relatively large (though not continuous) fieldof view can be obtained. A non-continuous image of sub-areas of theobject can be used during navigation stages.

FIGS. 6 a-6 f illustrates a rectangular area 80 of an object that iscompletely imaged by four different images that are shifted apart fromeach other. FIG. 6 a illustrates rectangular area 80. FIG. 6 billustrates aperture array 100 that includes rectangular shapedapertures. The apertures of aperture array 100 image one fourth ofrectangular area 80 at a time. FIGS. 6 c-6 f illustrate four shiftedapart images of sub-areas of rectangular area 80 that can be combined toprovide an image of rectangular area 80.

FIG. 7 a includes images of multiple sub-areas 68(1)-68(9) of an objectobtained through nine apertures. FIG. 7 b is a magnified image ofsub-area 68(5) of the object.

An aperture array can be manufactured in various manners includingdeposition and etch back. The deposition includes depositing one or moreultra thin membrane on an aperture array. The etch back includes etchinga plate in order to form multiple apertures.

It is noted that different aperture arrays or different aperture arrayscan be used in an interchangeable manner. Interface 3 can includemultiple aperture arrays and at a given point of time one (or more)aperture array can be illuminated by one or more electron beams.

FIG. 8 illustrates an interface 3 that includes three steps 111, 113 and115. Each step can include one or more apertures. The lowest step 111hosts the smallest apertures and the thinnest membranes 112 to providethe highest resolution. The distance between these apertures and theobject is smallest. The highest step 115 hosts the largest apertures andthe thickest membranes 116 to provide the largest field of view (but atthe lowest resolution). Intermediate step 113 includes membranes 114.

It is noted that FIG. 8 is a cross sectional view of interface 3.Interface 3 can have a annular shape (where steps 113 and 115 are ringshaped) but this is not necessarily so. For example—it can have arectangular shape.

Scanning Mechanism

An area of an object can be scanned by at least one of the following ora combination of both: (i) electrostatic scanning of the electron beam;(ii) mechanical scanning of the object with the electron beam in spotmode to form an image, which can be useful if one utilizes a very smallaperture and wants to generate an image with field of view larger thanthe size of the aperture; (iii) mechanical scanning of the microscopewith the electron beam in spot mode to form an image which can be usefulif one utilizes a very small aperture and wants to generate an imagewith field of view larger than the size of the aperture; (iv) mechanicalscanning of the aperture or window simultaneously with electrostaticscanning of the electron beam so that the electron beam follows thewindow position.

Detection Arrangement

According to various embodiments one or more detectors can be positionedwithin the vacuum environment and, additionally or alternatively, one ormore detector can be positioned in the non-vacuum environment. Acombination of both can also be provided thus one or more detector ispositioned in the non-vacuum environment while one or more otherdetectors are positioned in the vacuum environment.

FIGS. 1-3 b illustrate detectors that are located in the vacuumenvironment. A detector can, for example, be positioned inside thevacuum environment, between the object and an aperture or around theaperture. Locating the detectors in the vacuum environment canfacilitate small and even very small working distances between theobject and one or more apertures, thus contribute to the resolution ofthe image. Placing detectors in the vacuum environment also enables touse detectors that are less compatible with air such using coatingswhich easily oxides.

It is noted that using different detectors can provide more informationabout the illuminated area of the object and that multiple detectors canbe activated simultaneously.

According to an embodiment a pair of detectors is used for detectingelectrons. The pair includes a backscattered electron (BSE) detector anda secondary electron (SE) detector. The BSE detector can be locatedbetween the membrane and an objective lens. The BSE detector can have anannular shape that defines an opening enabling the primary beam to pass.The BSE detector can also be segmented to enhance topographyinformation. The SE detector can be an Everhart-Thornley detector (ETD)placed to the side of the primary electron beam. Secondary electrons areattracted to the ETD with a help of a biased collecting grid. The SEdetector can have an annular shape that defines an opening enabling theprimary beam to pass. The SE detector can also be segmented to enhancetopography information.

According to another embodiment a pair of detectors is used fordetecting electrons. The pair includes a BSE detector and a lightdetector. Both detectors operate simultaneously.

A parabolic mirror located between the membrane and the objective,having an opening enabling the primary electron beam to pass willcollect to light to a photomultiplier placed in the side of the electronpath. The mirror can be coated with a high secondary electron emittersuch as Csl. In this arrangement, backscattered electrons impinging thecoated mirror will generate secondary electrons which will be collectedby a SE detector

X-ray detector can be useful for material analysis. Integrating suchanalysis to an imaging engine permits localization of the object to beanalyzed enabling higher sensitivity for smaller object as opposed tomacroscopic analysis. Another possibility is to use emitted X-rays forimage generation which is commonly referred as X-ray mapping.

For analysis with low resolution where working distance of >100 micronscan be applied, the X-ray detector can be located outside the vacuumenvironment. It would be preferable to use an annular detector toincrease the collection efficiency.

For analysis with high resolution, where smaller working distance has tobe applied, let say <100 microns, the detector will be situated insidethe vacuum. If a side detector is used it can be in a configurationwhere backscattered electrons, secondary electrons and light can bedetected. An alternative arrangement where emphasis is on high X-raycollection efficiency is to use an annular X-ray detector such as amulti cell Silicon drift detector (SDD) manufactured by PNSensor.

Vacuum

SEM column 1 operates under vacuum. SEM column 1 can include multipledifferentially pumped spaces that are separated by a non-sealedaperture. It is noted that the sealing provided by interface 3 canrender such a partition unnecessary. It is noted that the vacuum can beprovided by one or more pump such as an ion pump, a turbo pump and thelike. Since the system is isolated a microscope can be designed withouta pump as done in a CRT.

Working Distance

There are three major effects associated with working distance:resolution, signal to noise and detection. For a given membrane andprimary beam energy, the resolution will decrease linearly with workingdistance due to the beam divergence introduced from scattering insidethe membrane. The second effect has to do with scattering of the beam inthe non-vacuum atmosphere, determined form the electron free mean path.The effect of electron scattering by the gas molecules is to deflectpart of the beam out of the original beam. The deflected part, oftenreferred as the “skirt”, forms a constant background signal. The centralpeak retains the beam spot with reduced amplitude. The third effect isalso associated with scattering but with the electrons emitted from thespecimen.

The scattering is a function of pressure, the gas molecules, electronenergy and the working distance. Ideally, it is desired to work in theregime below the electron mean free path, the average distance anelectron travels between collisions. For beam energies of few tens ofkeV, this distance is few tens of microns for molecules of air. The meanfree path is dramatically increased for molecules of He. For low energyelectrons, the mean free path is few microns. This will be manifested inthe detected signal: the signal of the high energy electrons oftenreferred as backscattered electrons will not be attenuated as opposed tothe secondary electrons which will suffer multi scattering events andthe signal will dramatically reduced.

For a given beam energy, the resolution can be increased by using athinner membrane and a shorter working distance.

STEM Mode

In this imaging mode, one detects the transmitted electrons through athin specimen. An electron detector is placed directly below thespecimen. In this case, maximal resolution is desired which can beachieved by using high beam energy and the controlling the workingdistance to be minimal by using an integrated spacer located around theaperture with height determining the working distance. Another advantageof using this spacer which is in contact with the sample is increasingthe resonance frequency of the system and therefore making it moreimmune to external noises.

The electrical current passing through the object as a result of aninteraction with the one or more electrical beam can be measured forexample by a Pico ampere meter.

The Non-Vacuum Environment

The environment between the sample and the column can be of anycomposition. In particular, in can be filled with air, at leastpartially filled with nitrogen or dry nitrogen where the efficiency oflight emission due to secondary gas excitation is high because theoxygen which is a quencher of this process is absent. The non-vacuumenvironment can be at least partially filled with inert gases and inparticular He or mixture of He where the mean free path of the electronis higher improving the signal to noise at larger worker distances.

Alignment of the Electron Beam

System 30 should align one or more electron beam to one or moreapertures through which the one or more electron beams should pass. Thealignment can utilize at least one of the following: (1) alignment coilsensuring that the one or more electron beams are aligned with the one ormore apertures; (ii) mechanical movement of the aperture array (or atleast the one or more relevant apertures); and (iii) mechanical movementof the objective or a permanent magnet relative to the aperture array.The advantage is that the moving part is not part of the vacuum sealing.

The mechanical movement of the aperture array (or relevant apertures)can be achieved by using a flexible connector between the aperture arrayand another part of the interface. The flexible connector can be movedby a motor (piezo motor, lineal motor and the like).

FIG. 9 a is a side view of an aperture array 81 that is connected viaflexible connector 40 to a rigid portion 41 of interface 3. The flexibleconnector 40 is moved by motor 42. It is noted that the motor can,additionally or alternatively, move aperture array 81.

According to an embodiment of the invention the motor is placed at ahigher position in order to provide smaller working distances. FIG. 9 billustrates a motor 42 that is connected to a rigid portion 44 ofinterface 3. The rigid portion 44 is connected to another portion 46 ofinterface 3 via flexible connector 45.

In the first configuration, the mass to be displaced is smaller butincorporating an actuator to move flexible connector 40 sets amechanical constraint on the working distance between the object and thepole piece. In the second configuration, a larger mass is displaced butthe working distance between the object and pole piece can be decreased.

Either one of the alignment methods mentioned above can be used also toselect one or more apertures of an aperture array.

In case of mechanical alignment of the aperture, the movement can bemotorized, controlled by a controller and positions can be calibrated orpreset to allow seamless work.

The flexible connector can be also used to control the distance betweenthe object and the aperture by moving the window in the directionperpendicular to the sample plane. This has the advantage of maintaininga fixed distance between the object and the aperture while moving asmall mass. FIG. 9 c illustrates two motors located at two oppositesides of flexible connector 40. These motors 42 are connected to twoopposing sides of flexible connector in a manner that allows them tointroduce a vertical movement.

The object can also contact the membrane, for example in the case whereit is a liquid or an emulsion. In this case, resolution will be maximalsince the electron scattering in the membrane are not reflected in spotbroadening.

Sample-Window Distance Measurement

The object aperture distance can be measured by at least one of thefollowing techniques: (i) Illuminating the object, measuring detectionsignal amplitude and comparing it to a calibration curve. Conveniently,the calibration curve is responsive to mean free path of electrons innon-vacuumed environment. If the distance between the object and theaperture is decreased then detection signals should increase at acertain rate until reaching the mean free path distance from which theincrement rate dramatically decreases. (ii) Measuring the counts ofemitted X-ray photons of the gas situated between the object and theaperture. The number of counts depends on the beam current and theinteraction volume. The interaction volume depends on that distance.(iii) Using a non electron beam related technique such as an integrateddistance measuring device based for example on capacitance measurement,triangulation and other common techniques used for example in opticalmicroscopy.

Various Configurations

FIGS. 1-3 b illustrate a stand alone system. It is noted that otherconfiguration are available. For example, system 30 can be integratedwith another tool or system, one or more detectors can be located in thenon-vacuum environment.

According to another embodiment of the invention system 30 can beintegrated with another tool.

FIG. 10 illustrates SEM column 1, other tool (such as an opticalmicroscope) 70 that are integrated together to provide system 73. SEMcolumn 1 includes interface 3 that is a part of vacuum chamber 72. Theother tool does not operate in vacuum thus does not require such achamber. Object 6 is supported by stage 76 that can move object 6 sothat is can be viewed by other tool 70 or by SEM column 1. Additionallyor alternatively, system 30 and another tool are used in order toobserve an object. The other tool can be of lower or higher resolution.Lower resolution tools can be optical microscopes. The opticalmicroscope can be used for locating regions of interest. The other tooland the scanning electron microscope column can be characterized bydifferent line of sights. The other tool can view a certain area of anobject and then sends information that enables the scanning microscopeto view that area. Methods for locating targets in a multiple columnconfigurations are known in the art and can be utilized for thispurpose. For example, the SEM G3 FIB of Applied Materials Inc. includesa SEM column and a Focused Ion Beam (FIB) column that are parallel toeach other. The FIB column and the SEM column are spaced apart from eachother but share information that enables these columns to view (atdifferent point in time) the same area.

It is further noted that the SEM column and the other tool can beoriented in relation to each other. Some dual column tools of FEI usesuch a tilted configuration.

According to various embodiments of the invention the other tool can bean optical tool operating in non-vacuum. In this case the SEM can beused to aid parameters tuning during recipe optimization, and to reviewresults for defect classification. Yet for another example, the SEM canbe used to characterize the elemental composition using X-rayspectroscopy of a defect found by the inspection tool.

According to various embodiments of the invention the SEM is part of atool that can include at least one of the following: (i) an atomic forcemicroscope, (ii) an optical review tool.

The SEM can be used for various purposes, including but not limited to:(i) image voltage contrast in air; (ii) electron beam lithography onphoto resist in air; (iii) high resolution imaging of wafers andprocesses which are incompatible with vacuum such as a photo resistbefore curing; (iv) image and analyze wafers and processes which areimpacted by the vacuum environment, or wafers and processes which aresensitive to formation of adhesion of a monolayer of contaminationmolecules; (v) excite X-ray emission for material analysis, whereas animage can be used to find a known location and generate an analysis onan exact location; (vi) excite X-ray emission for thickness measurement,whereas an image can be used to find a known location and generate ananalysis on an exact location; (vii) excite X-ray mission for densitymeasurement, whereas an image can be used to find a known location andgenerate an analysis on an exact location; (viii) image and analyze sidewalls, whereas an image can be used to find a known location andgenerate an analysis on an exact location, (ix) image and measurethickness of side walls, whereas an image can be used to find a knownlocation and generate an analysis on an exact location, and the like.

According to an embodiment of the invention the SEM can integrated in aprocess tool such as chemical vapor deposition (CVD), chemicalmechanical polisher (CMP), electrochemical deposition (ECP), an etcherand used to control process thickness.

FIG. 11 illustrates method 200 for observing an object that ispositioned in a non-vacuum environment, according to an embodiment ofthe invention.

Method 200 starts by stage 210 and optionally one or more of stages 212and 214.

Stage 212 includes introducing a gas mixture into the non-vacuumenvironment such as to improve the detection. The gas mixture caninclude, for example nitrogen or He enriched mixture.

Stage 214 includes aligning the at least one electron beam with at leastone aperture. Stage 214 can include aligning the at least one electronbeam with at least one aperture by mechanically moving the at least oneaperture. Additionally or alternatively, stage 214 includes deflectingthe at least one electron beam in multiple directions and counting theintensity of detection signals in order to determine when the at leastone electron beam are aligned.

Stage 210 includes generating at least one electron beam in a vacuumenvironment.

Stage 210 is followed by stage 220 of passing the at least one electronbeam through at least one aperture out of an aperture array and throughat least one ultra thin membrane that seals the at least one aperture.The at least one electron beam is directed towards the object. It isnoted that the optical axis of the at least one electron beam can beperpendicular (non-tilted configuration) or non-perpendicular (tiltedconfiguration) to the object.

Stage 220 is followed by stage 230 of detecting particles generated inresponse to an interaction between the at least one electron beam andthe object.

Stage 230 can include at least one of the following stages or acombination thereof: (i) detecting electrons generated in response tothe interaction between the at least one electron beam and the object;(ii) detecting photons generated in response to the interaction betweenthe at least one electron beam and the object; (iii) detecting X-rayemission generated in response to the interaction between the at leastone electron beam and the object; (iv) detecting particles by a detectorpositioned within the vacuum environment; (v) detecting particles by adetector positioned within the non-vacuum environment; (vi) detectingelectron current generated as a result of the interaction; and (vii)detecting Cathodoluminescence of the object, fluorescence markers orlight emitted due to electron excitation of gas molecules.

According to various embodiments of the invention stage 220 can includeat least one of the following stages or a combination thereof: (i)passing at least one electron beam through multiple apertures of theaperture array; (ii) passing an electron beam through the selectedaperture; (iii) passing at least one electron beam through at least oneaperture of the aperture array wherein apertures of the aperture arrayare positioned at a single horizontal plain; (iv) passing at least oneelectron beam through at least one aperture of the aperture array;wherein at least one aperture of the aperture array is positioned at adifferent height than at least one other aperture of the aperture array;(v) passing at least one electron beam through at least one membrane;wherein a certain membrane enables an acquisition of a higher resolutionimage than another membrane; (vi) performing a first iteration ofpassing and detecting and a second iteration of passing and detecting;wherein the first phase comprises passing at least one electron beamthrough at least one membrane to provide a first resolution image of atleast a portion of the object, and the second phase comprises passing atleast one electron beam through at least one other membrane to provide asecond resolution image of at least a portion of the object; and (vii)passing multiple electron beams through multiple apertures of theaperture array.

FIG. 12 illustrates method 300 for observing an object that ispositioned in a non-vacuum environment, according to another embodimentof the invention.

Method 300 starts by stage 310 of locating a region of interest of theobject using a low resolution imaging process.

Stage 310 is followed by stages 210-230. It is noted that at least oneof optional stages 212 and 214 can also be included in method 300.

FIG. 13 illustrates method 400 for observing an object that ispositioned in a non-vacuum environment, according to another embodimentof the invention.

Method 400 starts by stage 410 of utilizing an observation process thatis characterized by a different resolution range than the resolutionrange that is characteristic of stages 210-230.

Stage 410 is followed by stages 210-230. It is noted that at least oneof optional stages 212 and 214 can also be included in method 400.

It is noted that stages 210-230 can be followed by stage 410.

Conveniently, stage 410 includes at least one of the following or acombination thereof: (i) atomic force microscopy; (ii) opticalinspection process.

FIG. 14 illustrates method 500 for observing an object that ispositioned in a non-vacuum environment, according to another embodimentof the invention.

Method 500 starts by stage 510 of scanning at least one area of theobject by deflecting the at least one electron beam and introducing acorresponding mechanical movement of the at least one aperture throughwhich the at least one electron beam pass.

FIGS. 15 a-15 c illustrate multiple positions of an aperture andmultiple electrical beam orientations during a scan according to anembodiment of the invention. It is assumed that the object is scanned bya scan line 50. Scan line 50 is delimited by right end 51 and left end53. The center of scan line 50 is denoted 52. FIG. 15 a illustrates apoint in time during which electron beam 2 is deflected towards rightend 51 and aperture 55 is moved to a certain right position in order toenable electron beam 2 to pass through it. FIG. 15 b illustrates a pointin time during which electron beam 2 is deflected towards center 52 andaperture 55 is moved to a certain center position in order to enableelectron beam 2 to pass through it. FIG. 15 c illustrates a point intime during which electron beam 2 is deflected towards left end 53 andaperture 55 is moved to a certain left position in order to enableelectron beam 2 to pass through it.

Stage 510, includes repetitively executing stages 210-230 in order toobserve at least one sub-area of the object, executing stage 505 ofdeflecting the at least one electron beam and introducing acorresponding mechanical movement in order to facilitate an observationof another one or more sub-areas of the object and either repeatingstages 210-230 or ending stage 510.

It is noted that at least one of optional stages 212 and 214 can also beincluded in method 500.

Conveniently, stage 510 includes at least one of the following or acombination thereof: (i) scanning at least one area of the object bydeflecting the at least one electron beam and introducing acorresponding mechanical movement of the aperture array; (ii) scanningat least one area of the object by deflecting the at least one electronbeam and introducing a corresponding mechanical movement of the aperturearray; wherein a component that includes the aperture array is flexiblyconnected to another component of an interface that separates the vacuumenvironment from the non-vacuum environment; (iii) scanning multipleareas of the object by deflecting the at least one electron beam thatpass through multiple apertures of the aperture array; (iv) scanningmultiple areas of the object by deflecting the at least one electronbeam that pass through multiple apertures of the aperture array andintroducing a corresponding mechanical movement of the aperture array;(v) scanning an area of the object by deflecting the at least oneelectron beam by a deflector positioned within the vacuum environment.

APPENDIX A Transmission of Electrons Through a Membrane of Carbon

The interface between the vacuum where the electrons are traveling inthe column and the sample which is in non-vacuum is an ultra thinmembrane. The membrane has to fulfill the following criteria: (i)Mechanical strength: To withstand the pressure difference between vacuumand the non-vacuum atmosphere. The mechanical strength depends on thearea of the membrane, its thickness and its Young's modulus. For a givenmaterial, there is a tradeoff between the membrane thickness and itsarea. The maximal radial stress .sigma., for a circular window of radiusr and thickness t, separating a pressure differential p, is proportionalto .sigma..about.p r.sup.2/t.sup.2.

For a given yield stress .sigma..sub.yield and difference, the minimummembrane thickness t.sub.min depends on the radius of the foil:

t.sub.min.about.(pr.sup.2/.sigma..sub.yield).sup.1/2 (ii) Electronoptics: the membrane should have minimal influence on the primary beamto achieve maximal resolution. There are two factors affecting the spotsize: (ii.a) Scattering of the electrons due to the interaction with themembrane. The scattering depends on the primary beam energy, themembrane thickness and density. Optimally one would use the thinnestavailable membrane made from a low density material. This scatteringinduces broadening of the original spot size or a scattering angle.Thus, for a given membrane and accelerating voltage the spot diameter onthe sample plane increases linearly with the working distance betweenthe membrane and the specimen. (ii.b) Scattering of the electrons due tothe interaction with the non-vacuum atmosphere. This scattering and theissue of working under small working distance will be addressed later inthis document. (iii) Signal to noise ratio: to allow maximal primaryelectrons to reach the sample and maximal electrons and photons emittedfrom the sample to reach the detectors.

The transmission of electrons through a membrane of Carbon (density=2.25g/cm.sup.3) calculated for different energies and thicknesses usingH.-J. Fitting empirical formula (Journal of Electron Spectroscopy andRelated Phenomena 136 (2004) 265-272) and the transmission of X-rayphotons of some elements, calculated based on attenuation coefficienttaken from NIST database, are shown in Table 1.

According to Fitting, in the energy region below E.sub.0=10 keV therange-energy relation: R=900.rho..sup.−0.8E.sup.1.3.sub.0 was found withR in .ANG., .rho. in g/cm.sup.3, and E.sub.0 in keV.

Assuming absorbance/scattering is a serial in nature, one can deduce thetransmission for r: T(r)=0.01.sup.r/R.

The photon transmission is calculated according toI=I.sub.0exp.sup.−.mu.(.lamda.)d; where I.sub.0 is the number of photonsreaching the membrane, I is the number of photons transmitted, d is themembrane thickness. The quantity .mu.(.lamda.) with measuring unitcm.sup.−1 is called the linear attenuation coefficient and is dependentupon the wavelength .lamda. of the primary radiation and the density ofthe layer.

TABLE 1 transmission of electrons and photons of different energiesthrough membranes of Carbon of different thicknesses Energy Thickness(nm) (eV) 2 5 10 20 30 50 100 100 2.0E−02 5.7E−05 3.3E−09 1.1E−173.6E−26 3.9E−43 1.5E−85 300 3.9E−01 9.6E−02 9.3E−03 8.6E−05 7.9E−076.8E−11 4.6E−21 600 6.8E−01 3.9E−01 1.5E−01 2.2E−02 3.3E−03 7.4E−055.5E−09 800 7.7E−01 5.2E−01 2.7E−01 7.3E−02 2.0E−02 1.4E−03 2.1E−06 10008.2E−01 6.1E−01 3.8E−01 1.4E−01 5.3E−02 7.5E−03 5.6E−05

One can draw some general conclusions from the data: for primaryelectron beam with energy higher than 5000 eV membranes with thickness<100 nm are highly transmissible. For lower energies, the membranethickness has a big impact on the transmission. For X ray photons themembrane is highly transmissible. This is the case also for visiblelight.

As the guideline for the design of the microscope is resolution, theimmediate conclusion is that one has to use the thinnest membranepossible. This fortunately also favors optimized detection. However fromthe mechanical compatibility it implies that the membrane size islimited. The question is therefore how one can have an ultra thinmembrane with thickness of few nanometers or few tens of nanometers.Such membrane can stand the pressure difference if its area is small.One can see from Equation 2 that for a given material and pressuredifference, the decreasing the thickness scales linearly with decreasingthe window size. So the key to have high resolution electron beamtraveling in non-vacuum is to use a small area ultra thin membrane. Forexample, in images 6 and 17, a 30 nm SiN window with dimensions of50.times.50 micron was used. Technically, there are several ways oflimiting the area of a membrane. An ultra thin membrane on a support canbe generally realized by two different approaches.

The first approach is the deposition method. An ultra thin layer isdeposited or brought to a support structure. The simplest supportstructure is an aperture which determines the size of the availablemembrane. This approach is used in TEM grid preparation where Carbonlayers of thickness <10 nm are routinely placed on grids.

The second approach is the etch-back method. One deposit an ultra thinlayer A on a substrate B and then etches back B in a defined region toform an ultra thin window A on B. This is the case for example of SiN orSiO.sub.2 on Si. Both A and B can also be thinned by ion milling. Thisis seen in image 4 where an opening in the Si with a shape of a pyramid,which has been etched back to form a SiN window. A Cu grid, situated 15microns below the window in air, is clearly seen.

The size of the membrane or window determines the available field ofview of the microscope. When working with a high resolution microscope,the common practice is first to use small magnification (large field ofview) to locate the area or feature of interest, to bring the feature tothe center of the high resolution field of view using for example amoving stage and to change to a smaller field of view for a highresolution image of the feature. In the following a description of howto resolve the apparent conflict between field of view and resolutionenabling, the ease of use for locating an object in a big field of viewtogether with the limitation of having a small window yielding highresolution is given.

FIGS. 18 a-18 c are images of a grid obtained through a 10 nm thickcarbon membrane. These images also include a pyramid shaped aperture.Images 18 a-18 c differ from each other by the magnification level. Thefirst image is a small magnification image showing a grid. In this imagethe area of interest is found. The second image is a highermagnification image of the area of interest.

The present invention can be practiced by employing conventional tools,methodology and components. Accordingly, the details of such tools,component and methodology are not set forth herein in detail. In theprevious descriptions, numerous specific details are set forth, in orderto provide a thorough understanding of the present invention. However,it should be recognized that the present invention might be practicedwithout resorting to the details specifically set forth.

Only exemplary embodiments of the present invention and but a fewexamples of its versatility are shown and described in the presentdisclosure. It is to be understood that the present invention is capableof use in various other combinations and environments and is capable ofchanges or modifications within the scope of the inventive concept asexpressed herein.

What is claimed is:
 1. A method for observing an object that ispositioned in a non-vacuum environment, the method comprising: directingat least one electron beam generated in a vacuum environment through atleast one aperture of an aperture array sealed by at least one ultrathin membrane towards the object which is positioned in the non-vacuumenvironment, the at least one ultra thin membrane separating the vacuumenvironment from the non-vacuum environment; introducing a gas mixtureinto the non-vacuum environment whereby the mean free path of electronstherethrough is enhanced relative to air at atmospheric pressure; anddetecting, using a detector placed directly below the object, particlesgenerated as a result of an interaction between the at least oneelectron beam and the object wherein the enhanced mean free path ofelectrons due to the presence of the gas mixture provides enhancedsignal to noise ratio.
 2. The method according to claim 1 and whereinthe gas mixture comprises nitrogen.
 3. The method according to claim 1and wherein the gas mixture comprises a He enriched mixture.
 4. Themethod according to claim 1 and also comprising: scanning at least onearea of the object by: deflecting the at least one electron beam to passthrough the at least one aperture; and introducing a correspondingmechanical movement of the at least one aperture.
 5. A scanning electronmicroscope assembly for observing an object comprising: a scanningelectron beam source, located in a vacuum environment, adapted togenerate at least one electron beam; an interface between the vacuumenvironment and a non-vacuum environment in which the object ispositioned, the interface comprising an aperture array sealed by atleast one ultra thin membrane that is substantially transparent toelectrons and withstands a pressure difference between the vacuumenvironment and the non-vacuum environment; electron optics adapted todirect the at least one electron beam through at least one aperture ofthe aperture array and towards the object located in the non-vacuumenvironment; a gas introducer adapted to introduce a gas mixture intothe non-vacuum environment whereby the mean free path of electronstherethrough is enhanced relative to air at atmospheric pressure; and adetector placed directly below the object that detects particlesgenerated as a result of an interaction between the at least oneelectron beam and the object wherein the enhanced mean free path ofelectrons due to the presence of the gas mixture provides enhancedsignal to noise ratio.
 6. The scanning electron microscope according toclaim 5 and wherein the gas mixture comprises nitrogen.
 7. The scanningelectron microscope according to claim 5 and wherein the gas mixturecomprises a He enriched mixture.